US3528387A - Ion cleaning and vapor deposition - Google Patents

Description

United States Patent [72] Inventor Harold J. Hamilton Sylmar, California [21 Appl. No. 740,803

[45] Patented [73] Assignee [54] [ON CLEANING AND VAPOR DEPOSITION 2 Claims, 1 Drawing Fig.

[5 2] US. Cl

51 C23c 13/12 [50] FieldofSearch ..118/4849.5;

117/106D,107.1,107.2, 93.1; 219/1211, 121E.B;.

[56] References Cited UNITED STATES PATENTS 2,215,787 9/1940 Hailer Primary Examiner-Morris Kaplan Attorney-Joseph R. Dwyer ABSTRACT: Vacuum deposition apparatus for operation at low deposition pressures contains an ion gun in a separate chamber maintained at a higher pressure required for the production of a glow discharge. The ion gun is supplied with an inert gas to maintain its pressure and the ions are emitted into the deposition vacuum chamber through a small port generally aligned toward the substrate. The ions are used to bombard the substrate to clean its surface prior to deposition, or may bombard the substrate during or after the deposition step to improve adherence of the deposited film on the substrate.

VA CUUAI PUMP Patented Sept. 15, 1910 3,528,387

. VA CUUM PVUMP lNVE/VTOR M19010 1/ mm ATTORNEY This application is'a continuation ofapplication- Ser; No. 352,456, filed Marchl7, l964 ai1d now 'abandoned;

substrate may be cleaned by ion bombardment andcoatdby vacuumdeposition; a

To achieve a strongly adherent film by vacuum deposition it is necessary "that thesurfacehof the substrate 'be'free from all 5 contaminants at the instant of-ulepositionF'Elaborate chemical and physical cleaning" proce'dures' are presently required to achieve this condition. The removalof contaminants fromthe strate with only varying degrees of success; Thi's' is'due to the fact that ion bombardment must take place in a'cha'mber that is maintained at a relatively high pressure, such as l0- min of mercury or higher, whereas the vacuum deposition should take'place in the chamber maintained at a relatively low pressure, such as 10- mm of mercury or lower. During the period between ion bombardment at the relatively high pressure and the evacuation of the chamber to the relatively lovv pre ssure,

the substrate will again collect a contaminant film of oil, gas,

oxide, etc.

Heretofore, the most successful vacuum deposition processes involve elaborate chemical cleaning'of the substrate prior to its insertion in the vacuum chamber. The chemically cleaned substrate is then mounted within the chamber, the vacuum chamber is evacuated to pressure of the order of mm of mercury, the substrate is bombarded with ions produced by a cold cathode discharge to remove as much contaminant as possible, the chamber is then evacuated to'the lowest pressure obtainable, and finally the substrate is heated to a relatively high temperature (several hundred degrees centigrade) for a period of several hours to remove adsorbed gases and other contaminants which have accumulated during the period between the ion bombardment and the evacuation of the chamber to the vacuum deposition pressure. These elaborate procedures are time consuming, costly, not always effective, and impose serious limitations on the nature of the substrate.

In the present invention the substrate is not required to be subjected to elaborate chemical or physical cleaning prior to its insertion in the vacuum chamber. A substrate which has been cleaned with ordinary solvents and with ordinary precaution is attached to a support electrode in the chamber, the chamber is immediately evacuated to a relatively low pressure, such as 10- of mercury, and the substrate surface is cleaned of contaminants, without the application of externally applied heat, by ion bombardment immediately preceding, and during, the deposition of the coating. To achieve this ion bombardment at this relatively low pressure, an ion gun is inserted into the chamber. An inert gas, such as argon, is metered into the ion gun at a rate sufficient to permit the formation of a glow discharge .within the gun, yet insufficient to raise the chamber pressure above that which is required for vacuum deposition.

Briefly described, this invention comprises a main vacuum chamber which is maintained at the relatively low pressure required for vacuum deposition. Inserted through the wall of the main chamber is an ion gun having a small hole or exit port in its cathode which is exposed to the main chamber. The ion gun is supplied with an inert gas at a rate sufficient to maintain the internal chamber of the ion gun at a pressure suitable for the formation of a glow discharge within the gun. lons released through the exit port into the main vacuum chamber are rapidly accelerated toward the substrate because of a relatively high negative potential that is applied to the substrate support electrode. These high velocity ions bombard the substrate material and dislodge all contaminants from the surface. With proper design of the complete system, the main chamber can be maintained at a pressure low enough to provide a long molecular mean free path and at the same time a sufficiently intense ion beam or spray to decontaminate the substrate surface. Vacuum: deposition may 2 take .-;place ;,during.,g r im- :rnediatelyr after, the ion:bombardmentjofthe.substr e; .by resorting.to:conventional evaporation, techniques.

I v One object'of this inventiojn'is' to providevacuum depos'tion This invention relates} to coating apparatus, andjmore par- 5 1" ticularly to noveiand improved vacuum apparatus in=which a apparatuscapable' of cleaning and coating asubs tratew hm a f deposition apparatus capable of atomically cleanin w strate-and preventingicontamination priot to acuum .d position; I -15. g-Other sweet; will; taflggs'gtttg 'ffgoiii j ie deta led description and the drawingyin which the;,single figure .is a

sectional' view of a vacuumchamber andrion gunassem mbodying thisinvention. :7; lnvt heemliodirnent of this ,inventionshow .t e. w gi mawb asuit urnferal.lWdenotes-awacuum chamber which ble*..bell='jar, or,-as shown inthe drawings may, be aglass T joint 'having an inside diameter: of approXit tl SP? n h and. an uoveral r le g h pt I aPP ximat ly-.- 8 shss Q port of vacuum. chamber; 10 may be sealed .with an end plate- 12: through which; is rnounted ;a substrate mountingrod .14, which-maybeanyelectricallyconductive, material, such as *aluminunirSince-end .plate 12 is electrically :insulatedfrom other components in -the deposition. equipment ,by. the. glass vacuum chamber 10, it is not essential that mounting rod 14 be insulated fromend plate. 12. However, during the vacuum deposition process, the internal walls of vacuum chamber 10 will become coated and may cause end plate 12to be electrically conductive with other elements in. the deposition equipment. Therefore, it isdesirable that substrate mounting rod 14 I be insulated from end plate 12 by a suitable insulator 16. Substrate 18 may be mounted'within chamber 10 on mounting rod At the opposite port and sealing the end of chamber 10 is another end plate 20 to'which is mounted an ion gun 22,,a pair of electrically insulated conductors to supply electrical current to heater element. 24, and a third electrically insulated conductor which is connected to the cathode26 of ion gun 22.

The third port of vacuum chamber 10 is covered and sealed with an end plate 28, through which extends a pipe 30 connectedto vacuum pump 32.

As previously explained, ion gun 22 extends through end plate 20 so that its cathode 26 is within vacuum chamber 10. [on gun 22 may be constructed from any suitable electrically insulating material, such as glass tubing, and must have suffi-.

cient strength so that it can withstand low pressures. The end of the ion gun within vacuum chamber 10 is covered with an electrically conductive metallic cap or cathode electrode 26 which contains a small centrally located hole or exit port 27, the diameter of which is determined by the vacuum pump capacity, the desired chamber pressure and ion flux. ln practice, this may be of the order of 0.020 inch. Extending through the central bore of the ion gun to within the distance of approximately V4 inch of cathode 26 is an anode electrode 34 which may be a rod of any suitable electrically conductive material. While the principal requirement of the material of anode 34 is that it must be electrically conductive, consideration must be given to the thermal expansion properties of the anode since it must extend through, and be sealed to, the envelope of ion gun 22. In order to supply ion gun 22 with an inert gas, such as argon, a tubing may extend from ion gun 22 to a metering valve 36, which, as subsequently will be explained, is adjusted to provide ion gun 22 with a pressure suitable for the production of a glow discharge between anode 34 and cathode 26. The opposite end of metering valve 36 is connected to a source of inert gas.

in operation, a substrate 18 is washed to remove excessive contaminants and is mounted in vacuum chamber 10 on substrate mounting rod 14. Vacuum pump 32 is then started and vacuum chamber 10 is evacuated to a relatively low pressure suitable for vacuum deposition. This may be in the order of 10- mm of mercury, or lower. When the proper vacuum in chamber 10 is achieved, a potential of approximately +500 to 1,000 volts is applied toanode termin al38 through aEiiFfii" gun 22.

This introduction of an inert gas will increase the pressure within the ion gun; however, because vacuum pump 32 is in operation and because the small exit port 27 in cathode electrode 26 restricts the flow of gas into vacuum chamber 10, chamber can easily be maintained at a suitable vacuum deposition pressure. In order to produce a glow discharge between anode 34 and cathode 26 of ion gun 22, the pressure within the ion gun must be maintained at a relatively high pressure of approximately 10- to 10- mm of mercury. If desired, this pressure within ion gun 22 may be determined by connecting a suitable pressure gauge to the inner chamber or bore of ion gun 22, or may be more simply accomplished by merely increasing the flow of inert gas by the further opening of metering valve 36 until an anode current is observed on milliammeter 37, which is connected between anode 34 and its power source. When an anode current is observed, it is an indication that ionization within ion gun 22 has commenced and a current flow exists between anode 34 and cathode 26. Some of the positive ions produced in the gun escape through the exit port in cathode 26 and are accelerated toward the target substrate 18 because of the large negative potential applied to mounting rod 14. In general, these ions encounter little or no collisions with neutral gas molecules within vacuum chamber 10 because of the relatively low pressure, and as a consequence they acquire a very high velocity. When these ions strike the surface of substrate 18, their momentum and energy is transferred to molecules or atoms at the surface of the substrate, thus causing them to be ejected or sputtered from the surface. Any contaminant film on the surface of substrate 18 will thus be removed.

While substrate 18 is being cleaned by ion bombardment from ion gun 22, heater element 24 may be turned on so that sufficient heat is produced to vaporize a small amount of coating material which may be suspended directly from heater element 24 or placed into very close contact with the heating e lement. When the coating material has been boiled and evaporated, metering valve 36 may be closed and all of the voltage potentials removed from their associated terminals. The metallic vapor produced by the boiling of the coating material will then become evenly deposited upon the surface of the substrate 18.

it has been found that adherent films of aluminum upon glass microscope slides that have not been previously chemically cleaned, have been cleaned by ion bombardment and vapor-deposited within a total elapsed time of four minutes. This compares with a total elapsed time of several hours required by prior art methods.

It must be understood that various changes in configuration and arrangement of the various components of the equipment may be made without departing from the spirit of the invention.

lclaim:

1. An ion bombardment and vacuum deposition apparatus comprising:

a vacuum chamber;

electrically conductive substrate mounting means extending through a wall of said chamber;

means for evacuating said chamber to a vacuum deposition pressure; an ion bombardment gun having an anode electrode disposed within a housing and a cathode electrode forming a wall of said housing, said cathode electrode being located within said chamber and having an exit port to permit the escape of ions from said gun into said chamber; a gaseous feed means into said housing for maintaining said ion mb r me t g n ata su tab e ion a n pr means for applying an ion accelerating electrical potential between the cathode electrode of said ion bombardment gun and said electrically conductive substrate mounting means; and

electrical heating means within said chamber for evaporating a coating material.

2. The apparatus claimed in claim 1, further including means for applying an electrical potential between the anode electrode and the cathode electrode of said ion bombardment gun.

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